The present invention relates to a composition for reinforced and filled high density rigid polyurethane foam products and the method of making the same.
In the creation of a cellular polyurethane product by the reaction between an isocyanate and a polyol compound containing active hydroxyl groups, it is known that cellular cored products may be molded such as to have a continuous integral skin. The attraction of the integral skin foam molding process lies in its simplicity. The part can be molded in a one shot operation (including a prepolymer and a polyol) by mixing and pouring the reacting liquid components into a mold, which is contoured and textured to the shape and surface finish desired in the finished molded part.
It is also known that the physical properties of the resultant product can be improved by the inclusion of reinforcing fiber. It is also further known that the load bearing capability and density of the polyurethane foam product can be increased by the addition of a particulate filler.
The combination of a reinforcing fiber such as glass and a solid filler such as silica sand incorporated into a self-skinning rigid polyurethane foam, is here shown to provide a product having greater performance capability than that of an unfilled and unreinforced polyurethane composition. In fact, the use of both a particulate filler and reinforcing fiber when used with rigid polyurethane foam yields a product of greater performance than the incorporation of either the filler or fiber exclusively. A combination of advantages in cost and processing result from the urethane/fiber/filler composition as well.
Performance advantages with the use of reinforcing fiber include increased flexural modulus, an increase in heat distortion temperature, and an improvement in the mode of impact failure from one of glass like failure with unreinforced self-skinning rigid urethanes to one of a localized nature without crack propagation in reinforced samples.
In flammability testing, the glass fiber reinforced samples exhibit greater char strength and less tendency toward explosive cracking, shrinkage, and the release of small flaming particles than do the unreinforced samples. The dispersed fiber continues to hold the composition intact without contributing to the full content as the urethane polymer is consumed in the flame.
One problem, however, is that fiber strands tend to agglomerate and distribute themselves in a non-uniform manner while carrying with them large quantities of entrapped air. Such air entrapment yields products having uneven core cell structure and surface air bubbles which are unacceptable in products having a cosmetic requirement.
In addition to the lack of homogeneity in the formulation, further problems arise because of the tendency of the fibers to settle, as a result of normally low viscosity at the mixed materials thereby creating an uneven distribution of fibers in the molded product.
Some processes have been attempted wherein chopped glass fiber has been dispersed in either or both the isocyanate or polyol component of the two component system. It appears that such attempts have proven impractical due to dispensing equipment limitations; it is also believed that these processes yield a product wherein the glass fiber absorbs or isolates the isocyanate or polyol to such a degree that it is not possible to adequately mix and thereby react the polyol or isocyanate contained in the strands of the fiber. This, in turn, yields a product that when cured, still contains unreacted isocyanate or polyol. It would appear that by preventing the necessary wet out of the glass fiber filaments by the reacting foam components prior to gelation, there is a reduction of the higher physical property potential offered by the inclusion of a reinforcing fiber.
The problem then, has been in getting the glass fibers uniformly dispersed in the materials such as to have uniform dispersion in the final product. Even more serious, the ability to effectively include glass fiber in sensitive self-skinning polyurethane compounds has been limited by the ability to eliminate air entrapment or at least to minimize the effects of air entrapped as a result of the addition of the glass fibers.
It is also known that the inclusion of particulate fillers such as finely divided silica, Cab-O-Sil and the like, when dispersed in a rigid polyurethane foam composition, have served to increase the product density, and because of the lower cost of filler as compared to polyurethane foam components, reduce the cost per pound of molded product.
With the addition of the particulate fillers, such as silica, the problem has been in reaching the higher densities. Thus, while the addition of the filler increased density and stiffness the product loses elongation and flexural properties and is given to more brittle behavior under stress. Thus, products molded having high filler loading exhibit little tolerance for bending and impact thereby limiting their utilization in dynamic load applications. Yet the achievement of high density loading is desirable since dramatic cost savings on a per pound of product basis could be realized. In addition the higher density products lend themselves more readily for many applications where weight is a consideration, i.e. furniture items, architectural products, etc. In addition the inclusion of inorganic fillers, e.g. silica sand, into the conventional non-flame resistive high density rigid foams, creates a composition having high flame resistant properties.
In the present invention high filler loadings can be achieved along with the addition of reinforcing materials such as the glass fiber. The effects of air entrapment have been minimized and the glass fiber is uniformly distributed throughout the resultant product. While the higher filler loadings tend towards product embrittlement the glass fiber substantially improves the flexural and resilient characteristics of the product and provides a product having the desired density, stiffness and resilience.
Therefore, it is an object of the present invention to provide a rigid polyurethane foam product having substantially evenly distributed reinforcing glass fiber and having a substantially high loading of filler material such as silica.
In rigid polyurethane foam systems using the polyesters or polyethers the normal processing viscosity is in the range of 350 cps to 700 cps at 74.degree. F. At these viscosities the uniform addition of glass fibers is difficult since the fibers tend to settle during the time between the mixing of the fiber with the polyurethane materials and the time that gelation of the reacting composition occurs. While the addition of the glass fibers will increase viscosity, the loading of the mixture with the silica sand also causes an increase in viscosity. With increased viscosity the fibers (and silica) will more readily maintain their displaced position resulting from mixing and thereby assure uniform distribution in the final product. While an increase in viscosity is desirable the heavy loading will increase viscosity to the point where the flow characteristics are impeded causing problems in even distribution of the mixture in the mold. Thus in the process of the present invention the materials are heated to a temperature of around 115.degree. F to achieve a viscosity of 1200 cps to 3600 cps. At this viscosity the materials will still flow readily into the mold while maintaining the glass fibers in even distribution. Therefore, it is another object of the present invention to provide a process for making rigid polyurethane products having reinforcing with glass fibers and being heavily loaded with a silica sand filler in which the viscosity of the admixed materials is brought into a range of from around 1200 cps to 3600 cps by heating the mixture to a temperature of around 115.degree. F.
In the present invention blowing agents such as those commercially available from DuPont under the trademark Freon are used. However, in elevating the process temperature to around 115.degree. F, it has been found that the lower boiling point blowing agents, i.e. such as Freon 11, trichloromonofluoromethane, B.P. 74.8.degree. F are not suitable since they will begin to boil off before processing can effectively begin. Thus in the present invention a high boiling point blowing agent such as Freon 113, trichlorotrifluoroethane, B.P. 117.6.degree. F has been found suitable. Therefore, it is another object of the present invention to provide a process of the above described type in which a blowing agent having a boiling point above the pre-processing or mixing temperature of the starting materials. Of course, the boiling point is substantially below the in processing temperatures attained resulting from the exothermic reaction of the materials.
While the mixture of filler, such as silica sand, is desirable not all materials are suitable in combination with the glass fibers. The glass fibers contain substantial quantities of entrapped air. Unless the air is evenly dispersed or expelled the result will be structural non-uniformity of product, surface deformities, etc. Thus the quantity of glass fibers added could be severely limited. It has been found that with the addition of a particulate filler over a given mesh size the effects of air entrapment are eliminated or at least substantially minimized permitting substantial loading with glass fibers. With the addition of the filler substantially below the noted mesh size the air entrapment effects are not effectively limited. It has been found that the addition of commercially available silica sand with mesh sizes of from No. 30 U.S. sieve to No. 200 U.S. sieve provides the desired results of effectively limiting the effects of air entrapment. Therefore, it is another object of the present invention to provide a novel process for producing rigid polyurethane foam products having glass fibers by utilizing a particulate filler such as commercially available silica sand having mesh sizes of from No. 30 U.S. sieve to No. 200 U.S. sieve. It is also desirable to utilize the filler materials of the size noted above since higher loading can be obtained without increasing the viscosity of the mix to undesirable levels. Thus the use of finely divided particles, i.e. 2 microns or less not only do not solve the air entrapment problem but also seriously limit the amount of loading capability because of the effects on viscosity.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims.
As noted, the present invention deals with rigid polyurethane foam structures and to this end conventional compounds known in the art for the production of rigid polyurethane foam structures can be used. Thus in the preparation of rigid polyurethane foam products, any of a wide variety of hydroxyl terminated polyols may be used to react with an organic isocyanate and in the presence of a suitable solvent blowing agent (such as Freon 113 one of the Freons noted) produce the desired foamed product.
For the formation of the rigid polyurethane foam a highly branched polyol should be used or selected having a molecular weight, i.e. average weight per branch, of from about 300 to about 800. Examples of suitable polyol materials are the following:
Pluracol 565 (BASF Wyandotte Chemical)
a blend of polyols comprised of propylene oxide derivative of toluene diamine glycerine and propylene glycol -- with a Hydroxyl range of 319 - 339.
Plurocol PEP550 (BASF Wyandotte Chemical)
a polyoxypropylene derivative of pentaerythritol -- with a Hydroxyl range of 540 - 570.
Isonal 140
a highly crosslinked amine based propoxylated polyether -- with a functionality of 4.
The isocyanate can be selected from any one of the following suitable characteristic materials:
Tdi: tolylene diisocyanate (isomer positions being 2, 4 except as designated in text) PA1 Mdi: 4, 4' -- diphenylmethane diisocyanate PA1 Hdi: 1, 6 -- hexamethylene diisocyanate PA1 Ndi: 1, 5 -- naphthalene diisocyanate PA1 Dadi: 3, 3' dimethoxy -- 4, 4' -- biphenyl diisocyanate ("dianisidine diisocyanate") PA1 Todi: 3, 3' -- dimethyl -- 4, 4' -- biphenyl diisocyanate ("tolidine diisocyanate") PA1 Pdi: phenylene diisocyanate (isomer positions designated in text) PA1 Xdi: 4, 4' -- biphenyl diisocyanate ("xenylene diisocyanate") PA1 Isonate 580 PA1 Polymethylene polyphenyl isocyanate -- having a functionality of 2.7 -- a pure polymeric isocyanate PA1 Papi 105 PA1 polymethylene polyphenyl isocyanate -- having a functionality of 2.7
In practice, however, prepolymers of the above isocyanates are commercially available and are used. Thus in the present invention the following isocyanate prepolymers have been used:
It is known in the art to utilize a surfactant or nucleating agent which acts as a stabilizer in the bubble formation; the surfactant can be selected from known suitable materials such as silicone oil.
It is further known to utilize tertiary amine catalysts; a suitable such catalyst has been dimethyl aminoethanol. Other catalysts are the tin catalysts, i.e. (Stannous octoate).
In the process of the present invention, the temperature of the starting materials is raised in order to reduce overall viscosity. Hence a blowing agent should be selected having a boiling point higher than the pre-process temperatures to which the materials are raised. Fluorinated, halogenated, saturated aliphatic hydrocarbons may be used as blowing agents; as noted a suitable agent is: trichlortrifluorocthane, B.P. 117.6.degree. F (Freon 113).
The above listing of suitable materials is given by way of example only and not intended to be limiting since the present application does not deal with novel formulations of polyurethane forming materials but indeed utilizes known starting materials as normally used by those skilled in the art to produce rigid foamed polyurethane products. The invention here lies in the addition of glass fibers or the like as reinforcing members and silica sand or the like as a filler material such that commercially acceptable structural products can be realized.
As noted the mixture of sand, with glass fiber and polyurethane components minimizes the problem of air entrapment. When the mixing of the sand, glass and polyurethane components occurs, the sand acts to disintegrate or distribute the air, thereby creating a filled and reinforced foam having a more uniform cell structure as well as minimizing the surface voids which are undesirable from the cosmetic standpoint in rigid self-skinning products. It is found that the mixture referred to causes a more uniform mix consistency than is possible using glass fiber and polyurethane alone, and that the more uniform mix is achieved more quickly with the admixture of silica sand. While the applicant does not wish to be bound by any theory as to why this occurs, it is considered probable that the utilization of the proper filler particle size is such as to cause the subject filler to act as a mixing aid, and to effectively break up entrapped air which is included by the introduction of glass fiber. It has been found that the particle sizes of silica sand that perform satisfactorily are in the range of from U.S. sieve No. 30 to 200. With finely divided silica sand of substantially finer mesh, i.e. 2 microns, the advantages of minimizing effects of air entrapment are degraded. In addition, the viscosity of the starting mixture becomes excessive with appreciable loading hence restricting the amount of loading and product densities which can be practically achieved. With appreciably coarser particles the structural and finish characteristics are degraded.
It has been found that commercially available silica sand as provided by Ottawa Silica Products is suitable; produced by Ottawa Silica Products are three grades of silica sand, all of which appear to perform equally well in the subject process:
______________________________________ Percent U.S. Sieve No. On Sieve ______________________________________ No. 1 Mine Run 30 0 Mean Grain Fineness 61.5 40 2.2 50 19.8 70 30.8 100 32.5 140 13.5 200 0.9 No. 2 Coarse 30 0 Mean Grain Fineness 55.4 40 4.2 American Foundry Standard 50 30.7 70 32.8 100 23.3 140 8.4 200 0.5 No. 3 Fine 30 0 Mean Grain Fineness 72.5 40 0.5 50 5.2 70 20.4 100 47.2 140 24.1 200 2.1 ______________________________________
Loadings of from 10% to 75% by weight of final product of the above noted silica sand have been realized with the preferred range being 20% to 60%.
To achieve the high fiber and filler loadings desired and yet maintain the desirable material flow characteristics during processing, it is necessary to achieve a low viscosity in the polyol/isocyanate combinations being used to create the polyurethane composition. It also appears that the inclusion of silica sand as a filler prevents coalescence of the fluorocarbon blowing agent at the elevated product and tool temperatures being practiced with this invention.
Coalescence, or "ferns" as they are known in the industry are cosmetically and structurally unacceptable on most product surfaces, and are indicative generally of a mold surface that is too high in temperature when conventional liquid reactive urethane components have been dispensed therein for molding. It is believed that the inclusion of silica sand as a filler in the parts by weight outlined in this invention absorbs heat at the mold surface and also maintains the fluorocarbon in uniform dispersion to create discreet bubble sites and thereby uniform cell structure.
Variations in viscosity and result may be encountered when like weights of different types of glass chopped fiber are used. For instance, 10% of the total composition by weight of 1/4" chopped fiber having 500 0.00052 dia. filaments per strand with a 0.4% silane (silicone Hydride) sizing (such as PPG (Pittsburgh Plate Glass) No. 3390) will exhibit a lesser increase in the viscosity of the composition than will 10% by weight of 1/4" chopped fiber having 200 0.00052 dia. filaments per strand with a 1.5% silane sizing (such as PPG No. 3198). In processing, the 500 filament glass strand mixes into the urethane and sand compositions more rapidly with less inclusion of air than does the 200 filament glass strand, however in the molded part it is believed that less of the filaments of the 500 filament strand are wetted out than of the 200 filament strand fibers, and the physical properties are thereby reduced in the 500 filament strand reinforced products. The uncompacted bulk density of the 500 filament per strand fiber 1/4" is 50.19 lb/ft.sup.3 while the bulk density of the 200 filament per strand 1/4" fiber is 41.32 lb/ft..sup.3 (ASTM test std. D1895 Method A).
Further, viscosity variations are created when each of a variety of fiber lengths are employed. Generally, fibers having a higher bulk density, exhibit an ability to be included into the urethane composition in higher percentages with a lesser effect on the composition viscosity increase than do the fibers with a lower bulk density. For instance, 1/8" glass fiber strands create a lesser increase in viscosity than does 1/4" glass fiber strands of the same type when like weights of glass fiber are utilized. In general, the shorter the fiber length, the higher the bulk density and the lesser the increase in the viscosity of the composition.
It is desirable to have chopped fibers in the range of 3% to 25% by weight of the final product. The glass fibers are in the range of 1/32" to 1" in length. Best results were achieved with chopped fibers of 5% to 15% by weight of final product and preferably of 1/4" length of the 200 filament per strand noted above. With fibers shorter than 1/32" in length the structural benefits are degraded while with fibers exceeding 1" in length increases in viscosity of the starting materials become undesirable.
The objective of the present process is to provide structural products having a density of 10 to 80 lb/ft.sup.3 ; desirable foam products have a density of 15 to 45 lb/ft.sup.3 ; the structural products noted are not excessively brittle and can have excellent flexural and resilience characteristics as well as excellent surface cosmetic characteristics. The products are generally uniform in composition, i.e. free of excessive voids, blemishes. Since the quantity of urethane products per pound of product is reduced the cost of attaining such products is dramatically reduced. In addition, the viscosity of the working mixture is sufficiently low to greatly assist in the production of parts having the high densities noted.
In the process of the present invention then, the polyol component and isocyanate component are first heated to 115.degree. F. Next the polyol and isocyanate components are mixed vigorously for approximately 5 seconds. Prior to creaming and during the initial mixing the glass fiber and silica sand are mixed in. The mixed components will have a viscosity of approximately 1200 cps to around 3600 cps. This mixture is next dispersed into a mold cavity. The mold temperature is preferably 130.degree. to 140.degree. F. The mold is closed and the foaming proceeds to form the desired part. The following examples illustrate various combinations of filler and reinforcing materials in providing products having the desired characteristics.